(SHT 3) (SHT 3)
ELEV FEEL

FE
COMPUTER

CENTER HYD. SYSTEM  "ARM"
"ARM"
APL NOSE

APL NOSE
DN SOL

UP SOL
PRESSURE

BALLSCREW
RETURNELEV. FEEL PRESSUP ACTUATOR FWD
RATE CONTROL VALVE (SHT 3)
A
LEFT STAB
TRIM SHUTOFF
VALVE HORIZONTAL
STABILIZER
BRAKERETURN SECONDARYSECONDARY
PRESS OPERATEDBRAKEBRAKE
"ARM" VALVE
(PRESSURE(PRESSUREBRAKE
RELEASED) RELEASED) NULL
RELEASE GEARBOX APL NOSE UP APL NOSE DN
MANUALB (SHT 3)
BRAKE"CONTROL" VALVE
PRESS OPERATEDBYPASS
PREVENTSPRESSURE SW
BRAKE
CCWBACK-DRIVENULL
MOTORPRIMARYCASEBRAKE
DRAIN DISCS APL NOSE UP APL NOSE DN
PREVENTSCW
APL NOSE UP BACK-DRIVE APL NOSEDN
BRAKERETURNHYD
HYDMOTOR
MOTOR CASE DRAIN BRAKERELEASE
"ARM""ARM"APL NOSEAPL NOSEDN SOLUP SOL
(SHT 3)F E(SHT 3)
MOTOR
APL NOSE UP APL NOSE DN(SHT 3)LEFT STABILIZER TRIM CONTROL MODULE "CONTROL"
"CONTROL"
A
INTERNALS SAME AS LEFT STABILIZER
APL NOSE DN SOL APL NOSE UP SOL(SHT 3) B
DC
RIGHT STAB TRIM
TRIM CONTROL MODULE(SHT 3) (SHT 3)
BRAKE
SHUTOFF VALVEELEV
PRESSURE SW PRESS
RETURNFEEL
DC
SYSTEM PRESSURE

RIGHT HYD SYSTEM
"CONTROL""CONTROL"ELEV FEEL CMPTRAPL NOSEAPL NOSE
RETURN DN SOL UP SOL
(SHT 3) (SHT 3)METERED PRESSURE
Horizontal Stabilizer Trim System Schematic
Figure 7 (Sheet 4)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ALTERNATE STAB TRIM ú

 27-41-00
 SWITCHES ON THE CONTROL STAND  ú ú 01 Page 22 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

 (4)  
In the manual-electric mode, stabilizer operation is controlled by dual stabilizer trim control wheel switches on the captain's and first officer's control wheels. The switches, when activated, send ARM and CONTROL signals to the left and right SAM's. Dual auto/manual transfer relays and autotrim priority relays in each SAM transmit the signals to ARM and CONTROL solenoid valves in the left and right STCM's. Operation of both valves on each module results in release of secondary brake and application of hydraulic power to the respective motors. The output of the drive hydraulic motors is summed by the differential gearbox and converted to stabilizer motion by the ballscrew actuator. Stabilizer motion continues until the stabilizer trim control wheel switches are released or the electric trim limits are reached. Both switches must be moved in same direction for stabilizer operation.

 (5)  
AIRPLANES WITH STAB TRIM LEVERS ON THE CONTROL STAND; in the manual-mechanical mode, stabilizer operation is controlled by dual mechanical STAB TRIM control levers on the control stand. Lever movement is transmitted by a separate mechanical ARM and CONTROL cable system to both the left and right STCMs. The dual inputs to both STCMs release the secondary brakes and power the drive hydraulic motors. The output of the hydraulic motors is summed by the differential gearbox and converted to stabilizer motion by the ballscrew actuator. Stabilizer motion continues until the levers are released or until the mechanical travel limits are reached. Both STAB TRIM control levers must be moved in the same direction for stabilizer operation.

 (6)  
AIRPLANES WITH ALTERNATE STAB TRIM SWITCHES ON THE CONTROL STAND; in the alternate-electric mode, the stabilizer operation is controlled by dual switches on the control stand. The switches send electrical signals to the left and right STCMs. The dual inputs to the two STCMs release the secondary brakes and power the hydraulic motors. The output of the hydraulic motors is summed by the differential gearbox and converted to stabilizer motion by the ballscrew actuator. Stabilizer motion continues until the switches are released or until the electrical travel limits are reached. Both switches must be moved in the same direction for stabilizer operation.

 (7)  
AIRPLANES WITH STAB TRIM LEVERS ON THE CONTROL STAND; the STAB TRIM control levers have priority over any other control mode by mechanically positioning two servo valves in the STCMs. When the levers are operated, the valves hydraulically interrupt any other trim signals. The stabilizer trim control wheel switches have priority over all the other electric trim modes, except when in autoland mode (3 FCCs and autoland switches selected). Automatic stabilizer trim has priority over the mach/speed trim mode. The mach/speed trim mode is selected as a default mode when neither the automatic nor manual-electric trim is engaged.
　
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